Grinding wheel



Sept. 19, 1939.. H. w. WAGNER E, AL 2,113,462

GRINDING WHEEL Original Filed NOV. 4, i935 lEpim f6 b1/newton HERBERT W.WAGNER KENNETH l Wmv-00MB :BY @@UTQ flltofwwn Patented sept. 19, 1939UNITED STATES PATENT OFFICE Y` GRINDING WHEEL sachusetts Originalapplication November 4, 1935, Serial No. 48,181. Divided and thisapplication April 1, 1938, Serial No. 199,534

6 Claims.

This invention relates to grinding wheels, and particularly to grindingwheels made of abrasive grains bonded together by vitrified ceramicmaterials, rubber, shellac, resin, the articial resinoids, etc.

When a grinding wheel of a given mass is rotated, each element of thewheel has a certain centrifugal force which acts outwardly. This forcedepends upon the speed at which the wheell is rotating, the distance ofthe element from the center of the disk and the mass per unit of volumeof the wheel. This centrifugal force sets up stresses in therotatingwheel and so causes strain and deformation which tend to break the wheelwhen it is rotated at a certain maximum or breaking speed. Similarly,the act of grinding on the periphery of the wheel causes frictional heatto be generated, and this results in a temperature gradient existingbetween the periphery of the wheel and the center which also sets updisruptive stresses within the wheel. Hence, both the centrifugal forceand the frictional heat combine to cause wheel breakage. Because ofthese two factors, each type of grinding wheel is limited in its use toa certain standard wheel speed which should not be exceeded because ofdanger to the operator, although the efficiency of a grinding operationis increased by raising the wheel speed. I

'Ihe primary object of this invention is to increase the standardgrinding speed for a given type of wheel by strengthening the wheel sothat it will have the same factor of safety at the higher speeds, and toprovide a grinding wheel structure which may be rotated rapidly andsubjected to a high frictional heat during a grinding operation withoutdanger of breakage of the wheel. Other objects will be apparent in thefollowing disclosure.

The tenslonal stresses within a -grindingrwheel due to the centrifugalforce and to frictiial heat are both maximum at the center of the wheel.The standard grinding wheel has a hole at its center for mounting thesame on an arbor or spindle.l The principal stresses within the wheelare in' two directions,l radial and tangential; but at the edge of thehole of a rotating Wheel, the radial stress is zero. Hence, the maximumstress occurring at the edge of the hole is tangential in direction.When this tangential tensional stress equals the tensile strength of thematerial, then a radial crack starts at the edge of the hole and growsuntil the periphery of the wheel is reached. This happens whether thestress be due to centrifugal force or to heat applied at the peripheryof the Wheel, and the stresses due to these two forces combine by simpleaddition to cause wheel breakage.

This invention contemplates fortifying a grinding wheel by omitting thecentral hole 5 thereof and by providing bonded abrasive material, inthat position of maximum stress, which has a higher intrinsic strengthythan has the outer zone.

Referring to. the drawing; which illustrates various embodiments of thisinvention;

Fig, 1 is a plan view, partly broken away, of an imperforate grindingwheel having two annular zones, the outer one being suitable forgrinding purposes and the inner zone constructed for strengthening thewheel;

Fig. 2 is a fragmentary plan view of a Wheel having small mounting holesarranged and located remote from the irnperforate center of the wheel;

Fig. 3 is a similar fragmentary view showing a two zone wheel providedwith mounting holes;

Fig. 4 is a fragmentary sectional view showing how an imperforate wheelmay be mounted by cernenting it to a supporting member;

Fig. 5 is a sectional fragmentary view showing how a supplemental bondmay be applied to a wheel of uniform structure so as to form a two zonewheel as shown in Fig. 3; and

Fig. 6 shows hows a vitriiied wheel may be 30 strengthened during thering operation.

As shown in Fig. 1, a grinding wheel may be made as a two' zonestructure in which the outer zone I0 is adapted for the normal grindingoperations and the inner zone I2 serves to strength- $6 en the grindingwheel. This wheel may be provided with small mounting holes I4 (Figs. 2and 3) which are arranged concentric to the axis but remote from thecenter of the wheel and are of such sizesand locations that the wheel 40is not materially weakened in its structure by the presence thereof.Bolts are adapted to pass through these holes and secure the wheel on asuitable flat faced backing plate. Such a wheel may, however, be mountedin other ways, such l, as being made entirely imperforate and cementedto a backing plate. I

The structure of the grinding wheel may be made in accordance with thestandard methods of manufacture, except as regards leaving out thecentral hole of the wheel and fortifying the central zone. The wheelcomprises abrasive grains, such as crystalline alumina, silicon carbide,boron. carbide or diamond of suitable grit sizes, which are cemented orbonded together by standard bonds, such as vitrifled ceramic materials,vulcanized rubber, heat set resinoid,.shellac, resin, sodium silicate,etc. The invention is particularly applicable to thevltried wheelsbecause of their being relatively fragile although of great commercialvalue. The vitriflable ma-l terials comprise ball clay, slip clay,feldsp'ar, kaolin, flint and various other materials compounded insuitable proportions which are intermixed with the abrasive grains in aplastic condition for molding the wheel shape. The molded wheel is redin a ceramic kiln at a suitable ltemperature to mature the bond to aglassy or porcelanic condition. Rubber and resinoid wheels are heated atlower temperatures to vulcanize the rubber or to convert the plasticresinoid to a hard infusible body. Various well lknown procedures areadopted for the purpose of setting the particular bond chosen. Oneprimary d'fference over the prior art lies in so shaping the wheels asto omit from such wheels the central spindle hole. If outer mountingholes I4 are provided, these may be made either in the plastic moldablemass prior to heat setting the bond or by drilling the holes in thefinall wheel, structure after the bond has been matured or heat set.Various expedients may be adopted for this purpose. By such methods, weprovide a wheel having no central` hole i. e., having a continuousimperforate structure throughout the central zone of high stress,without regard to the natural porosity of the wheel.

We may further strengthen such a wheel by impregnating the pores in thecentral portion I2 (Fig. l) of a standard one zone wheel of uniformstructure with a resinoid or other matekor frictional heat than will awheel made wholly of the outer zone composition and structure. In such awheel, the moduli of elasticity of the two zones may be substantiallyequal and the materials are so chosen as to quantity and kind that thedrying and ring shrinkages do not cause detrimental strains or cracks atthe junction between the two zones.

Such a wheel may comprise an outer zone made of vitrified ceramicbonding material and suitable abrasive grains cemented together therebyand an inner zone likewise made of abrasive or other granular materialcemented together by vitrifled ceramic material, but in which the grainsare much smaller or the bond is present in a larger amount in the innerthan in the outer zone, so that the central zone is the stronger of thetwo. The outer zone -may be made, for example, of crystalline aluminavabrasive grains of 16 grit size bonded by means of 2% ounces of astandard ceramic bond per pound of the abrasive. The central zone may bemade of similar abrasive grains of v36 grit size, and 31/4 ounces of thegrain bond per pound of abrasive may be employed. When these twomixtures have been molded together into the annular shapes illustratedand fired in a ceramic As a further example, the outer zone may be' madeof crystalline alumina abrasive of between 30 and 36 grit size, and 3%ounces of bond to the pound of abrasive may be employed. In

-the inner zone, the abrasive may be made up of a mixture of one half of60 grit, one quarter.

of 'l0 grit and vone quarter of 80 grit size, and the ceramic bond maybe used in the proportion of 31/2 ounces per pound of abrasive.

The inner zone will be of such size radially that it will receive aconsiderable proportion of the stress within the wheel, and preferablyextend to such distance from the center that the mounting holes I4 maybe located as above defined within this inner zone. That is, themounting holes of the wheel may be located at approximately 40% of thedistance outwardly from the center, as indicated in Figs. 2 and 3, andthe material of this inner zone will extend suciently far beyond theseholes so that the localized zones of stress around each of the mountingholes will be ,located substantially wholly within this inner zonematerial. It is satisfactory to locate these holes at least 1/ inchinside of the periphery of the inner zone. Thus, we may produce a wheelwhich is far stronger than either thel one zone no-hole wheel or the twozone wheel having a central mounting hole, whereby the wheel will standa very high rate of rotation as well as a high temperature gradient fromthe periphery to the center of the wheel. In order to show thesuperiority of this two zone no-hole wheel over the standard wheel, two

wheels were made as follows: A two zone wheel was made with the outerzone of crystalline alumina abrasive of 36 grit size and bonded to whatis known as grade J on the Norton scale of hardness. This outer zoneemployed 3A of an ounce of standard ceramic bond per pound of abrasive.The inner zone without a central hole was made of 60 grit size of thesame abrasive and with the same bond in the proportions of one ounce ofbond per pound of abrasive so that the grade of the central zone wasgrade K. In that wheel the inner zone had a radius of 41/2 inches andthe outer periphery of the wheel a-radius of ten inches. Four 1/2-inchholes were located four inches from the center and inch bolts employedin mounting the wheel. For comparison, a single zone wheel with a 3-inchcentral hole was made to grade J of 36 grit size so as'to correspondwith the structure of the outer zone of the first wheel. This singlezone wheel broke at the speed of v11,890 surface feet per minute, whilethe two zone wheel broke at 'a speed of 18,850 surface feet per minuteor approximately 58% higher breaking speed. An average increase ,of 40to 50% in this breaking speed is thus easily obtained. I

As shown in Fig. 4, the no-hole wheel may be mounted on a metal or otherrigid plate I8 by means of a layer of vulcanized hard or soft rubber 20.This plate I8 is adapted to be suitably fastened as by means of bolts22' to a hub 24 constructed for mounting on the end of a wheel spindleof a standard grinding machine. The plastic rubber may be placed betweenthe side of the completed grinding wheel and the iron plate and thensubjected to heat and pressure to cause the rubber to stick to the ironplate and to permeate the surface pores of 'the wheel where it isvulcanized in position. Various expedients may be adopted for thepurpose of increasing the cohesion of the rubber cement with the wheelface and the metal plate. Likewise, a resinoid cement may be adopted forthis purpose, such as the unconverted Bakelite phenol aldehydecondensation product which is applied in a plastic condition between themounting plate and wheel and is set to a hard Yinfusible condition bymeans of heat, as is well understood in the art.

m Another way of strengthening the no-hole Wheel involves impregnatingthe central portion of the wheel with a strengthening bond or cement. Aporous wheel of uniform structure which has no central hole may be madeof desired grade and structure in accordance with the prior art methodsbut may be provided with mounting holes as indicated above. The centralzone of this wheel is then impregnated with a strengthening agent whichis capable of i'llling the pores of the wheel suiiciently and ofadhering to the surfaces thereof so as to materially aid the wheel inwithstanding the stresses of the grinding, but the outer zone is leftuniilled. Of the various materials which may be employed for thatpurpose, vulcanizable rubber and a plastic unconverted resinoid of atype of the Bakelite phenolic condensation product are preferred,although'other materials such as rosin, sodium silicate, and other wellknown cementitious materials or grinding wheel bonds may be. employedfor the purpose. The wheel may be impregnated with this material by anysuitable procedure. For example, as shown in Fig. 5, the wheel may haveannular plates 30 and a ring 22 mounted so as to enclose the outergrinding zone which is not to be impregnated to any material extent.Then the strengthening material may be flowed or forced into the poresof the wheel in the central zone thereof. For instance, melted rosin ora liquid resinoid or sodium silicate may be poured onto the two wheelsides and allowed to permeate the pores by the natural capillary action.A vacuum mayI be applied to the wheel face to cause the material topermeate the same. If rubber is used, a layer of the plastic rubbercompounded with sulfur in the right proportions may be forced underpressure and heat into the wheel faces and thus caused to permeate thesame. The rubber may also be employed as a solution or in any othersuitable form for the purpose. After the strengthening material has lledthe pores of the central zone sumciently, it is caused to set to a hardcondition, as by vulcanizing the rubber compound or converting theresinoid to the infusible condition by the application of sufficientheat for the purpose. The wheel may be preheated prior to theintroduction of the lling material in order to cause it to flow morereadily, or one may preheat only n the inner zone by means of a iiame orby heating the central zone within an oven while the outer zone issuitably insulated by thermal insulation. .Other expedients may beadopted for the purpose. By this means, the' vulcanized rubber or theresinoid or other medium employed is 'caused to grip the pore surfacesand to be sufficiently integral therewith so that it aids the wheelmaterially in resisting 'the stress set up by centrifugal force and theheat of grinding. 'I'hus the wheel is strengthened in thatimperforatecontinuous zone where the maximum stresses are present. 'I'his internalstrengthening zone may be sufciently Wide so that it will receive themajor -portion of thev stress, but the rosin, etc. should preferably notextend materially into the zone used for grinding. The impregnatedzonemay extend throughout approximately 40% of the radial distance withinthe wheel, as indicated in Fig. 1.

Likewise, a vitrified grinding wheel made of abrasive grains cementedtogether by vitried' ceramic bonds may be so made as to have no holethere supported while red within a ceramic kiln.

The wheel 34 may be covered with refractory clay 36 or other suitableheat insulating material in the manner shown in Fig. 6 so that the clayis increasingly deeper going from the center of a wheel outwardlytowards its periphery. Thus the wheel will radiate heat more quickly atthe central zone during the cooling operation than it will on the outerportion and the center will set first from a plastic to a solidcondition and thereafter the still plastic outer zone will shrink as itsets and so impose a compressional strain upon the central zone of thewheel. 'Ihis strained condition within the lwheel material tends toresist the stresses set up by rotation and heat during use of the wheel.

The grinding wheel may be so shaped and mounted that it will grind onits peripheral face or on a at side face. The wheel may therefore beshaped as a diskor in any other form which is foud best suited for agiven grinding operation. The principles of this invention applyirrespective of the shape, kind, type, size or other physicalcharacteristics of the wheel as well as to the various wheel structuresmade by using the different type of abrasive and of bond in any suitableproportions and structural arrangement.

'Ihis case is a division of our co-pending, application Serial Number48,181 filed November 4, 1935. A

We claim:

1. A composite grinding wheel comprising a body of bondedgranularabrasive material having an outer annular zone of requiredgrinding characteristics and an inner zone integral therewith which iscontinuous and imperforate at the wheel center', said inner zonecomprising abrasive material and a bond which has a greater strengththan has the outer zone and being of such size that the wheel may berotated safely at a rate in excess of the maximum safe speed for a wheelmade solely of the outer zone material and structure! 2. A compositegrinding wheel comprising an outer annular zone of bonded granularabrasive material of required grinding characteristics, and

an inner strengthening zone of bonded granular material of predetermineddifferent characteristicsintegrally united with the outer zone and whichis continuous andimperforate at the wheel center in the zone of maximumstress, the inner zone containing sufficient granular material of afiner grit size than has the average grain in the outer zone and thebond and granular material being of such character and proportionsrelative to those of the outer zone that the inner zone has a higherstrength than has the outer zone and such a rupturaldeformation andmodulus of elas- `:f5

ticity that the composite wheel will withstand greater stress due to therotation or peripheral heat than will a. wheel made wholly of the outerzone composition and structure.

3. A grinding Wheel according to claim 1 in which the bond and theabrasive material in the inner zone are so constituted and proportionedthat the ruptural deformation and modulus of elasticity are such thatthe wheel will withstand a greater stress due to rotation or peripheralheat than will a wheel made solely of the outer zone `structure andmaterial.

4. A grinding wheel comprising abrasive grains united by a bond into arequired grinding structure and which is continuous and imperforatethroughout the central high stress zone, said wheel being impregnatedwith a strengthening material within the-central zone of the wheel.

5. A grinding wheel of the type covered by claim 1 in which the centralzone comprises bonded abrasive material united as a porous structurewhich is impregnated with a heat set strengthening material.

6. A grinding wheel comprising abrasive grains united by a bond as aflat sided disk of the required grinding structure having an outer zoneproviding a peripheral grinding face and an inner strengthening zoneintegral with the outer zone which is continuous and imperforate at theWheel center and has a stronger structure and so is more resistant thanis the outer grinding zone to the stresses of centrifugal force andfrictional heat at the periphery of the Wheel, a supporting plate and acementitious medium uniting one face of the plate integrally to one sideof the wheel solely within the inner zone of high strength.

. HERBERT W. WAGNER.

KENNETH F. WHITCOMB.

